|Publication number||US5526324 A|
|Application number||US 08/515,580|
|Publication date||Jun 11, 1996|
|Filing date||Aug 16, 1995|
|Priority date||Aug 16, 1995|
|Also published as||WO1997007496A1|
|Publication number||08515580, 515580, US 5526324 A, US 5526324A, US-A-5526324, US5526324 A, US5526324A|
|Inventors||William B. Cushman|
|Original Assignee||Poiesis Research, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (4), Non-Patent Citations (4), Referenced by (15), Classifications (5), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
This invention relates to acoustic absorption and damping materials, and more particularly, to acoustic absorption and damping materials that utilize a piezoelectric phenomenon to convert mechanical energy into electrical energy and to subsequently dissipate the converted energy as heat.
2. Description of Related Art
Absorbing or damping unwanted acoustic or vibrational energy involves converting that energy into another form, usually heat. At the molecular level, the only distinction between heat energy and acoustic or vibrational energy is the randomness of the vector directions of molecular displacements. Acoustic and vibrational energy is highly correlated with large numbers of molecules displacing at the same time and in the same direction. Heat in a particular object may well have the same or more energy than propagating acoustic or vibrational energy, but the motion of the molecules is random with the mean molecular displacement at any given location being near zero.
Two primary techniques are available for randomizing the vector directions of the molecules in a matrix material propagating acoustic or vibrational energy. Cushman, et al. (U.S. Pat. No. 5,400,296) teach the use of two or more species of particles with differing characteristic impedances in a matrix material to promote random internal reflections at boundaries within the matrix material and the subsequent increase in probability that phase cancellation at adjacent or nearby locales can take place. Single particle species may also be used in this manner, but with less effect. Phase cancellation effectively randomizes the vector direction of molecular movement where it occurs. A second approach involves the careful choice of materials that exhibit a high degree of internal hysteresis. This internal hysteresis is thought to be caused by metastable molecular energy levels within the material. Propagating acoustic or vibrational energy may boost a particular molecule into a higher energy level, thus subtracting that energy from propagating energy, where the molecule remains for some time before randomly returning to its original energy level. For a discussion of this effect see Hartmann and Jarzynski, "Ultrasonic hysteresis absorption in polymers," J. Appl. Phys., Vol. 43 , No. 11, November 1972, 4304-4312.
Instead of randomizing molecular displacements to dissipate propagating acoustic or vibrational energy, some of this energy can be removed by converting the mechanical energy of sound or vibration into electrical energy utilizing the piezoelectric effect. A piezoelectric material such as polyvinylidene fluoride (PVDF) may be polarized and a coating of a conductive material such as aluminum applied to produce a piezoelectric transducer that will convert acoustic energy into electric energy, thus facilitating removal of converted energy from the system. This approach is reported in a recent issue of the Japan New Materials Report (May-June, 1995, p 9). In this report acoustic energy reductions of up to 90% are claimed in material specimens only 10 to 30 microns thick. However, the need to polarize the material and apply conductive electrodes to tap off the electrical energy produced limits the usefulness of this technique.
Accordingly, the object of the instant invention is to provide an improved acoustic absorption and vibration damping material utilizing the piezoelectric effect that may be injection molded, compression molded, or extruded without additional processing.
This and additional objects of the invention are accomplished by mixing electrically conductive particles or strands into a piezoelectric matrix material. The electrically conductive particles or strands act as small localized electrical short-circuits within the matrix material and effectively dissipate the electric charges produced by piezoelectric effect from the pressure of acoustic or vibrational energy as heat. All energy thus converted into heat is subtracted from the original acoustic or vibrational energy, resulting in acoustic absorption and/or vibration damping.
In the following Description of the Preferred Embodiments and the accompanying drawings, like numerals in different figures represent the same structures or elements. The representation in each of the figures is diagrammatic and no attempt is made to indicate actual scales or precise ratios. Proportional relationships are shown as approximations.
FIG. 1 shows a shows a piezoelectric matrix material of the instant invention with a plurality of embedded electrically conductive particles.
FIG. 2 shows a piezoelectric matrix material of the instant invention with a plurality of embedded electrically conductive strands.
The parts indicated on the drawings by numerals are identified below to aid in the reader's understanding of the present invention.
10. Piezoelectric matrix material.
11. Electrically conductive particle.
12. Electrically conductive strand.
A preferred embodiment of the instant invention is shown in FIG. 1 with electrically conductive particles. In FIG. 1, 10 is the piezoelectric matrix material of the instant invention and may be any piezoelectrically active material. A preferred piezoelectric matrix material is polyvinylidene fluoride (PVDF). The electrically conductive particles, 11, of FIG. 1 are randomly distributed within the piezoelectric matrix material, 10, and act as electrical short-circuits for the piezoelectrically active matrix material. Current flowing in the electrically conductive particles, 11, will cause them to heat due to their resistance. The heat produced in the electrically conductive particles will be dissipated into the piezoelectric matrix material but will have no specific orientation relative to the propagation direction of the acoustic or vibrational energy that produced the electricity that causes heating. That is, the molecular movement of the heat that results indirectly from the piezoelectric effect of the matrix material is random and, additionally, somewhat phase-delayed due to the thermal inertia of the electrically conductive particles. Thus, the correlated molecular movement of propagating acoustic or vibrational energy within the piezoelectric matrix material of the instant invention is decorrelated into heat. A preferred material for the electrically conductive particles is graphite.
A preferred embodiment of the instant invention is shown in FIG. 2 with electrically conductive strands. In FIG. 2, 10 is the piezoelectric matrix material of the instant invention and may be any piezoelectrically active material. A preferred piezoelectric matrix material is polyvinylidene fluoride (PVDF). The electrically conductive strands, 12, of FIG. 2 are randomly distributed within the piezoelectric matrix material, 10, and act as electrical short-circuits for the piezoelectrically active matrix material. Current flowing in the electrically conductive strands, 12, will cause them to heat due to their resistance. The heat produced in the electrically conductive strands will be dissipated into the piezoelectric matrix material but will have no specific orientation relative to the propagation direction of the acoustic or vibrational energy that produced the electricity that causes heating. That is, the molecular movement of the heat that results indirectly from the piezoelectric effect of the matrix material is random and, additionally, somewhat phase-delayed due to the thermal inertia of the electrically conductive particles. Thus, the correlated molecular movement of propagating acoustic or vibrational energy within the piezoelectric matrix material of the instant invention is decorrelated into heat. A preferred material for the electrically conductive strands is graphite.
Many modifications and variations of the present invention are possible in light of the above teachings. For example, any matrix material with piezoelectric activity may be used and any electrically conductive particles, strands, or long fibers, may also be used. It is therefore to be understood that, within the scope of the appended claims, the instant invention may be practiced otherwise than as specifically described.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3515910 *||Nov 12, 1968||Jun 2, 1970||Us Navy||Acoustic absorbing material|
|US3614992 *||May 26, 1969||Oct 26, 1971||Us Navy||Sandwich-type acoustic material in a flexible sheet form|
|US4628490 *||Dec 24, 1985||Dec 9, 1986||The United States Of America As Represented By The Secretary Of The Navy||Wideband sonar energy absorber|
|US5400296 *||Jan 25, 1994||Mar 21, 1995||Poiesis Research, Inc.||Acoustic attenuation and vibration damping materials|
|1||Hartmann & Javzynski "Ultrasonic hysteresis absorption in polymers" J. Appl. Phys. vol. 43, No. 11, Nov. 1972, 4304-4312.|
|2||*||Hartmann & Javzynski Ultrasonic hysteresis absorption in polymers J. Appl. Phys. vol. 43, No. 11, Nov. 1972, 4304 4312.|
|3||*||Japan New Materials Report, May Jun. 1995, p. 9.|
|4||Japan New Materials Report, May-Jun. 1995, p. 9.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5706249 *||Apr 1, 1996||Jan 6, 1998||Cushman; William B.||Panel spacer with acoustic and vibration damping|
|US5745434 *||Jan 9, 1997||Apr 28, 1998||Poiesis Research, Inc.||Acoustic absorption or damping material with integral viscous damping|
|US5754491 *||Feb 24, 1997||May 19, 1998||Poiesis Research, Inc.||Multi-technology acoustic energy barrier and absorber|
|US5911930 *||Aug 25, 1997||Jun 15, 1999||Monsanto Company||Solvent spinning of fibers containing an intrinsically conductive polymer|
|US6228492||Sep 23, 1997||May 8, 2001||Zipperling Kessler & Co. (Gmbh & Co.)||Preparation of fibers containing intrinsically conductive polymers|
|US6386317 *||Dec 21, 1999||May 14, 2002||Nissan Motor Co., Ltd.||Sound-absorbing duct structure|
|US7837008 *||Sep 27, 2005||Nov 23, 2010||The United States Of America As Represented By The Secretary Of The Air Force||Passive acoustic barrier|
|CN101981343B||Nov 12, 2008||Jul 2, 2014||罗伯特·博世有限公司||Apparatus and method for the excitation and/or damping and/or detection of structural oscillations of a plate-shaped device by means of a piezoelectric strip device|
|CN102700203A *||Jun 15, 2012||Oct 3, 2012||哈尔滨工业大学||Carbon fiber composite material laminated plate with piezoelectric damping and preparation method thereof|
|CN102700203B||Jun 15, 2012||Oct 29, 2014||哈尔滨工业大学||一种具有压电阻尼的碳纤维复合材料层合板的制备方法|
|CN103963398A *||Apr 29, 2014||Aug 6, 2014||中国航空工业集团公司北京航空材料研究院||Dual-functional toughening-damping intercalation material and product prepared from same|
|CN103963398B *||Apr 29, 2014||May 4, 2016||中国航空工业集团公司北京航空材料研究院||一种双功能插层材料及制品|
|CN104527173A *||Dec 5, 2014||Apr 22, 2015||中简科技发展有限公司||Composite damping layer toughened thin layer and preparation method thereof|
|EP0964181A3 *||Jun 5, 1999||Nov 20, 2002||DaimlerChrysler AG||Method and device to influence vibrations resulting from an engine-driven vehicle|
|EP0964387A3 *||Jun 5, 1999||Mar 20, 2002||DaimlerChrysler AG||Method and apparatus for influencing window-generated noise|
|U.S. Classification||367/1, 181/294|
|Apr 2, 1996||AS||Assignment|
Owner name: POIESIS RESEARCH, INC., FLORIDA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CUSHMAN, WILLIAM B.;REEL/FRAME:007878/0954
Effective date: 19960328
|Jan 4, 2000||REMI||Maintenance fee reminder mailed|
|Jun 11, 2000||LAPS||Lapse for failure to pay maintenance fees|
|Aug 15, 2000||FP||Expired due to failure to pay maintenance fee|
Effective date: 20000611